1. Technical Field
The present invention generally relates to heat exchangers and more specifically to a joint for joining an end of a coolant tube to a header.
2. Background Art
In an effort to extend the duration and durability of heat exchangers, much development has been focused upon improving the joint formed between the ends of coolant tubes and the header plate. For example, early on, those skilled in the art began forming ferrules or collars circumferentially about the apertures extending through the header in an effort to provide additional support between the header and the end of the tube. Further developments included mechanical locking measures such as providing staked portions between the end of the tube and ferrule, as shown in U.S. Pat. No. 4,334,703 to Arthur et al. Yet another development is shown in U.S. Pat. No. 5,036,913 wherein portions of the ferrule are welded to portions of the end of the coolant tube.
A major disadvantage to prior art tube-header joints is that the strength of the ferrule and the end of the tube are compromised in the process of securing the two together. For example, the temperature created by welding a portion of the ferrule and tube end weakens the metallurgical strength of both the ferrule and tube end at locations adjacent the weld area, thus resulting in failure over time.